1. Field of the Invention
The present invention relates to a model aircraft, such as a non-powered model glider, with wireless earth-to-craft control and having aboard an altitude change indicating device for signalling the existence of such change to the operator. Hereinafter a model aircraft of this type will be referred to as a model aircraft of the type set forth.
2. Description of the Prior Art
In the German journal "Modell", Neckar-Verlag, Villingen 1972, pages 426 to 428 and 479 to 484, a model aircraft of the type set forth is described utilizing an evacuated spring-biased capsule of the kind usually found in a weather-glass for sensing ambient air pressure. Preparatory to use in flight, the instrument requires adjustment to the prevailing barometric pressure at a starting point, which is done by setting a spring of the spring-biased capsule. A core of magnetizable metal is mounted on a deflectable wall of the capsule and is displaced relative to an induction coil in accordance with altitude change, thereby changing inductivity of the coil. Since the coil is part of an electric oscillating circuit, frequency of oscillation is changed due to wall movement. This change of frequency is signallized to a wireless transmitter, then transmitted to the earth and transformed into audible signals in a receiver carried by the operator. The signals are repetitive sounds similar to those of a Geiger counter. An increasing frequency of the sounds indicates climbing of the aircraft and a decreasing frequency indicates descent thereof.
A disadvantage of these altitude change indicating means is the great expense of a wireless transmitter and receiver. Another disadvantage is that many countries require an official permission for model aircraft-to-earth radio transmission but not vice versa for earth-to-aircraft radio transmission.